H. pylori causes gastritis, duodenal ulcers and is strongly linked to gastric cancer, but most infections are asymptomatic. No group of GI signs and symptoms have been shown to predict infection or associated disease. At present, no validated non-invasive tests exist to diagnose active H. pylori infection in children. Despite this, many clinicians test for H. pylori in children with gastrointestinal (GI) symptoms and will treat if the infection is "found". The urgent need for a rational approach to treatment of H. pylori in children is underscored by the fact that more than 11 million U.S. children are infected, using a conservative prevalence estimate of 15%. A randomized controlled trial of the effect of H. pylori eradication on GI symptoms in children is clearly needed. Before conducting such a trial, important preliminary validation studies are required. This study will test the overall hypothesis: that it is feasible to use non-invasive tests and a symptom assessment instrument (SAI) to determine the presence/absence of H. pylori infections in children with GI symptoms and can be used as diagnostic surrogates for the more invasive endoscopy and biopsy. Since commercial serology tests are not accurate in children, aim 1 will be to determine the feasibility of using the non-invasive 13C urea breath test and stool antigen test, preformed at the time of previously scheduled endoscopy and biopsy, to accurately detest active H. pylori infection in children and thus be considered as potential effective surrogate tests for diagnosis. Preliminary data on the sensitivity, specificity, positive and negative predictive value of these tests will also be compared using the standards for diagnosis established by the FDA. Aim 2 will be to determine the feasibility of using a pediatric gastrointestinal (GI) symptom assessment instrument (SAI), administered at the time of endoscopy, to evaluate GI symptoms of children with symptomatic H. pylori infection. Preliminary data will be obtained on the ability of the SAI to measure the severity of signs and symptoms based on endoscopic and histologic findings.